笛卡尔积和from子句中的选择

Question

我需要在from子句中使用select，但我会继续使用笛卡尔积。

select 
customer.customer_name
,orders.order_date
,order_line.num_ordered
,order_line.quoted_price
,part.descript
,amt_billed
from (select order_line.num_ordered*part.price as amt_billed
    from order_line
    join part
    on order_line.part_num = part.part_num
    ) billed
,customer
join orders
on customer.customer_num = orders.customer_num
join order_line
on orders.order_num = order_line.order_num
join part
on order_line.part_num = part.part_num;

不要太费力地看着其余部分。我已经知道，如果删除from子句中的子选择和select子句中的amt_billed，我就不会得到笛卡尔积。我做错了什么导致笛卡尔积？

Answer 1

笛卡尔积的原因是，您没有加入带有orders或Part表的子选择。

首先，您不需要sub-select

SELECT customer.customer_name, 
       orders.order_date, 
       order_line.num_ordered, 
       order_line.quoted_price, 
       part.descript, 
       order_line.num_ordered * part.price AS amt_billed 
FROM   customer 
       JOIN orders 
         ON customer.customer_num = orders.customer_num 
       JOIN order_line 
         ON orders.order_num = order_line.order_num 
       JOIN part 
         ON order_line.part_num = part.part_num;